This invention relates to a flexible or floppy disk (which may be abbreviated to "FD") for use in a removable type magnetic recording/reproducing device such as a flexible or floppy disk drive (which may be abbreviated to "FDD").
As is well known in the art, the flexible disk of the type described comprises a magnetic recording medium and a jacket for receiving the magnetic recording medium. The magnetic recording medium comprises a flexible thin sheet composed of synthetic resin, a magnetic recording layer formed on a surface of the flexible thin sheet, and a coating layer formed on the magnetic recording layer.
On the other hand, the flexible disk drive of the type described is a device for carrying out data recording and reproducing operations to and from the magnetic recording medium of the flexible disk loaded therein. In recent years, the flexible disks have been more and more improved to have a larger storage capacity. Specifically, development has been made of the flexible disks having the storage capacity of 128 Mbytes (which may be called large-capacity FDs) in contrast with the flexible disks having storage capacity of 1 Mbytes or 2 Mbytes (which may be called small-capacity FDs). Following such development, the flexible disk drives have also improved to accept the large-capacity FDs for data recording and reproducing operations to and from the magnetic recording media of the large-capacity FDs. Furthermore, the large-capacity FDs have been more improved to have a larger storage capacity of 256 Mbytes, 512 Mbytes, . . . , and so on.
Throughout the present specification, flexible disk drives capable of recording/reproducing data for magnetic recording media of the large-capacity FDs alone will be referred to as high-density exclusive type FDDs. On the other hand, flexible disk drives capable of recording/reproducing data for magnetic recording media of the small-capacity FDs alone will be called low-density exclusive type FDDs. Furthermore, flexible disk drives capable of recording/reproducing data for magnetic recording media of both the large-capacity and the small-capacity FDs will be called high-density/low-density compatible type FDDs. In addition, the high-density exclusive type FDDs and the high-density/low-density compatible type FDDs will collectively be called high-density type FDDs.
The low-density exclusive type FDD and the high-density type FDD are different in mechanism from each other in several respects, one of which will presently be described. In either FDD, a pair of magnetic heads is supported by a carriage which is driven by a drive arrangement to move in a predetermined radial direction with respect to the magnetic disk medium of the flexible disk loaded in the flexible disk drive. The difference resides in the structure of the structure of the drive arrangement. More specifically, the low-density exclusive type FDD uses a stepping motor as the drive arrangement. On the other hand, the high-density type FDD uses a linear motor such as a voice coil motor (which may be abbreviated to "VCM") as the drive arrangement.
Now, description will be made as regards the voice coil motor used as the drive arrangement in the high-density type FDD. The voice coil motor comprises a voice coil and a magnetic circuit. The voice coil is disposed on the carriage at a rear side and is wound around a drive axis extending in parallel to the predetermined radial direction. The magnetic circuit generates a magnetic field in a direction intersecting that of an electric current flowing through the voice coil. With this structure, by causing the electric current to flow through the voice coil in a direction intersecting that the magnetic field generated by the magnetic circuit, a drive force occurs in a direction extending to the axis on the basis of interaction of the electric current with the magnetic field. The drive force causes the voice coil motor to move the carriage in the predetermined radial direction.
Another difference between the low-density exclusive type FDD and the high-density type FDD resides in the number of revolutions of a spindle motor for rotating the magnetic recording medium of the flexible disk loaded therein. More specifically, the low-density exclusive type FDD may rotate the magnetic recording medium of the small-capacity FD loaded therein at a low rotation speed of either 300 rpm or 360 rpm. On the other hand, the high-density type FDD can admit, as the flexible disk to be loaded thereinto, either the large-capacity FD alone or both of the large-capacity FD and the small-capacity FD. As a result, when the large-capacity FD is loaded in the high-density type FDD, the spindle motor for the high-density type FDD must rotate the magnetic recording medium of the large-capacity FD loaded therein at a high rotation speed of 3,600 rpm which is equal to ten or twelve times as large as that of the small-capacity FD.
In the meanwhile, the large-capacity FD generally has an external configuration identical with that of the small-capacity FD. Specifically, both of the large-capacity and the small-capacity FDs have a flat rectangular shape of a width of 90 mm, a length of 94 mm, and a thickness of 3.3 mm in case of a 3.5-inch type. However, the large-capacity FD has a narrower track width (track pitch) than that of the small-capacity FD. As a result, it is difficult for the large-capacity FD to position a magnetic head of the high-density type FDD on a desired track in the magnetic recording medium thereof in contrast with the small-capacity FD. Accordingly, a servo signal for position detection is preliminarily written in the magnetic recording medium of the large-capacity FD.
In addition, the flexible disk is called a disk cartridge in the manner known in the art. The disk cartridge comprises the magnetic recording medium and upper and lower shells for receiving the magnetic recording medium with a space left therebetween. A combination of the upper and the lower shells is referred to as the jacket. The upper and the lower shells are provided with upper and lower head windows, respectively, to permit an access to the magnetic recording medium by a pair of magnetic heads. The magnetic recording medium is made of a magnetic material having a flexibility. That is, as described above, the magnetic recording medium comprises the flexible thin sheet composed of synthetic resin, the magnetic recording layer formed on the surface of the flexible thin sheet, and the coating layer formed on the magnetic recording layer.
The magnetic recording medium has an annular shape with a media circular opening formed at its center to be concentric with a center axis of the magnetic recording medium. The magnetic recording medium is supported at the periphery of the media circular opening by a supporting hub through a double-sided adhesive tape called an A ring in the art. The supporting hub is called a metal hub or a center hub.
A conventional supporting hub is generally made by press molding of a metal plate. Specifically, the supporting hub has a substantially dish shape and comprises a concave portion at its center thereof and an outer circumferential portion at the periphery of the concave portion. That is, the concave portion consists of a cylindrical portion and a circular bottom portion. In addition, the outer circumferential portion is called a flange portion which is formed at the upper end of the cylindrical porition. The jacket or the lower shell has a shell circular opening which serves to expose the concave portion of the supporting hub to the exterior of the jacket. In addition, the supporting hub serves to chuck the flexible disk at a disk holder table of the flexible disk drive. Specifically, the supporting hub has a hub center hole formed at its center and a chucking hole formed at a position eccentric with the hub center hole. The disk holder table is rotatably driven by a spindle motor. The spindle motor comprises a spindle shaft to which the disk holder table is fixed at an upper portion thereof. The disk holder table is provided with a chucking pin formed thereon. The spindle shaft and the chucking pin are inserted to the hub center hole and the chucking hole to rotate the magnetic recording medium of the flexible disk in a predetermined rotation direction.
In the conventional supporting hub, a lower surface of the outer circumferential portion is adhered by the A ring to an upper surface of the magnetic recording medium at the periphery of the medium circular hole. Specifically, the concave portion has a concave diameter while the outer circumferential portion has an outer diameter. Accordingly, the media circular opening of the magnetic recording medium has a medium opening diameter which is greater than the concave diameter and is smaller than the outer diameter. Inasmuch as the concave diameter of the concave portion is substantially equal to 25 mm in case of the 3.5-inch type flexible disk, the medium opening diameter of the magnetic recording medium is greater than 25 mm in case of the 3.5-inch type flexible disk. In addition, the supporting hub may be adhered to the magnetic recording medium by the use of an adhesive instead of the A ring.
As described above, the magnetic recording medium is adhered to the supporting hub. Thus, only the upper surface of the magnetic recording medium is supported by the supporting hub. In other words, the magnetic recording medium is supported only at its one surface. As a result, the magnetic recording medium may suffer occurrence of stuck wrinkles. Such stuck wrinkles occur remarkably in the vicinity of medium stuck positions where the magnetic recording medium is adhered to supporting hub. When the magnetic heads of the flexible disk drive are brought into contact with the magnetic recording medium for writing/reading operations, the contact (hereinafter called "head touch") becomes unstable in the presence of such stuck wrinkles. In this event, it is difficult for the magnetic heads to perform stable data writing/reading operations upon the magnetic recording medium and it results in occurrence of writing/reading errors. This is because the writing/reading operations for the magnetic recording medium by the magnetic heads are carried out in a data writing/reading area in the vicinity of the medium stuck positions. Such problem is particularly serious when the magnetic recording medium is rotated at a high speed, for example, at 3,600 rpm in case where the flexile disk is the large-capacity FD. This is because the large-capacity FD has a narrower track width (track pitch) than that of the small-capacity FD as mentioned before.